The Structures And Characteristics Of New Optical Devices Based On Two Dimensional Photonic Crystals

Since the discovery of photonic crystals more than a decade ago, the research on them has made rapid and steady progress. With artificial periodic structures, photonic crystals can generate photonic band gaps that forbid light propagation at certain frequency ranges. Utilizing photonic band-gap (PBG) effect, a lot of active and passive optical devices are designed based on photonic crystals. They not only have small sizes than ever and are easily integrated, but also have great charming characteristics compared with the traditional optical devices, which may eventually pave the way for the next generation optical communication systems.Due to the practical application of the increasing optical networking nodes in wavelength division multiplexing (WDM) systems, using the coupled mode theory in time, the optical devices are designed based on two dimensional photonic crystals (2D PCs) in this paper, including the add and drop filters, 2×2 directional coupler switch, optical splitter and Mach_Zehnder interferometer(MZI). These devices have ultra compact sizes and great merits compared with the corresponding conventional devices. Subsequently, the reconfigurable optical add/drop multiplexer (ROADM) device is proposed based on 2D PCs. It consists of the channel add and drop filters, two bends with 120°bending angles, and a 2×2 directional coupler switch. By integrating these optical devices based on 2D PCs, it is firstly proved that the ROADM device can be designed. The numerical results demonstrate that the device can be used for dynamically wavelength routing in optical networking node.In this paper, by means of the coupled mode theory in time, the coupling systems between photonic crystal line defect waveguides and point defect micro-cavities are analyzed in detail and the time evolution of the micro-cavity amplitudes are described. At the same time, the foundational numerical theories of PCs are discussed on the basis of the classical Maxwell's equations. The calculations methods of Plane-wave Expansion (PWE) method and Finite Difference Time Domain (FDTD) method, which are applied to numerically analyze the 2D PCs are studied in detail.A novel three-port add/drop filter is engineered based on the 2D PCs. In the structure, two micro-cavities are used. One is used for a resonant tunneling-based channel add/drop filter. The other is used to realize wavelength-selective reflection feedback in the bus wave-guide, which consists of a point defect micro-cavity side-coupled to a line defect waveguide based on photonic crystals. Using coupled mode theory in time, the conditions to achieve 100% drop efficiency are derived thoroughly. According to the theoretic analysis, such the filters are realized on the basis of the 2D PCs with square and triangular lattice, respectively. The numerical simulation results by using the finite-difference time-domain (FDTD) method imply that the design is feasible. Subsequently, a six-channel drop filter is engineered, and larger than 95% drop efficiencies are obtained in all channels.The ROADM device are firstly designed by integrating these optical devices based on 2D PCs. Using the coupled mode theory in time, it is found that the channel add operation is the'time-reversed'process of the drop operation. So two operations can be combined into the optical add/drop multiplexers (OADM). The chirp structures are introduced in the 2×2 directional coupler switch to improve its extinction ratio, which is obtained by merely changing the radius of the border holes next to the guiding region gradually. The switch operation is realized by changing the refractive index of these holes in chirp and coupling regions of directional coupler. The R-OADM integrate these optical devices in 2D PCs with a triangular lattice of air holes, including the channel add and drop filters, two bends with 120°bending angles, and a 2×2 directional coupler switch. The operations of ROADM are confirmed based on the numerical results, which can be used for dynamically wavelength routing in the optical networking node.In addition, a novel power-splitter scheme with wide operation bandwidth based on mode splitting of directional coupling waveguides is presented. The operation principle of the splitter is that only one of the super-modes splitting from the directional coupler can propagate through coupling region in the frequency range of interest. Based on the structure, a novel photonic crystal Mach-Zehnder interferometer switch with wide operation bandwidth is achieved as the additionalπphase shift is introduced in one of arms. The reason is the mode recirculation-enhanced effect in the MZI, which is realized by engineering different splitter and combiner structures.